Redis preloading fails when exec() returns false

[LeanderFS]

Preconditions and environment

• Magento 2.x
• Redis 6.0.10 (Probably every version of Redis)
• phpredis

Steps to reproduce

1. Install Magento 2 as normal
2. Enable Redis in env.php under cache->frontend->default
3. Make sure to set backend option to Magento\\Framework\\Cache\\Backend\\Redis
4. Set id_prefix and preload_keys
5. Run bin/magento cache:clean

This might not reproduce the issue in a lot of the cases because in normal scenarios there would be no issues. This issue arises as an edge-case when \Magento\Framework\Cache\Backend\Redis::load is being called.
$this->preloadedData = array_filter(array_combine($this->preloadKeys, $redis->exec())); expects the second parameter of array_combine to be an array, but $redis->exec() can return false in some cases. Leading to an unexpected exception and inability to run cache:clean or similar commands that preload keys in Redis.

Expected result

I expect the cache:clean command to finish without an error.

Actual result

The following exception is thrown:
array_combine(): Argument #2 ($values) must be of type array, bool given

Additional information

The issue is not immediately apparent, but makes more sense when you look into what the \Cm_Cache_Backend_Redis class is doing, which is the class the Magento Redis adapter extends from. The Cm_Cache_Backend_Redis class pipes the requested method through to Credis_Client, which in turn pipes the request to phpredis. The method signature for exec() in Credis_Client tells us that the return value will always be of the type array, but when checking the implementation in phpredis, exec() can return false. Causing the preloading in Magento to fail.

Release note

No response

Triage and priority

• Severity: S0 - Affects critical data or functionality and leaves users without workaround.
• Severity: S1 - Affects critical data or functionality and forces users to employ a workaround.
• Severity: S2 - Affects non-critical data or functionality and forces users to employ a workaround.
• Severity: S3 - Affects non-critical data or functionality and does not force users to employ a workaround.
• Severity: S4 - Affects aesthetics, professional look and feel, “quality” or “usability”.

[m2-assistant]

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[LeanderFS]

@magento I am working on this

[m2-assistant]

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[engcom-Hotel]

Hello @LeanderFS,

Thanks for the reporting and collaboration!

Just to confirm, you are mentioning phpredis below:

but when checking the implementation in phpredis, exec() can return false. Causing the preloading in Magento to fail.

Are you talking about this repo https://github.com/phpredis/phpredis?

If yes, then we have gone through with the documentation of phpredis for the exec method and it is mentioned there that it can return false, please refer to the below screenshot for reference:

I have taken this screenshot from the below file:

https://github.com/phpredis/phpredis/blob/35a7cc094c6c264aa37738b074c4c54c4ca73b87/docs/Redis.html#L591

Thanks

[LeanderFS]

Hi @engcom-Hotel

I can confirm I was talking about the phpredis/phpredis repository. I should've mentioned that in the initial message.

The documentation you've linked is exactly what I mean. The PR linked to this issue fixes the scenario where exec() would return false.

[engcom-Hotel]

Thanks @LeanderFS for the response.

We are confirming this issue by looking into the phpredis documentation.

Thanks

[github-jira-sync-bot]

✅ Jira issue https://jira.corp.adobe.com/browse/AC-8809 is successfully created for this GitHub issue.

[m2-assistant]

✅ Confirmed by @engcom-Hotel. Thank you for verifying the issue.
Issue Available: @engcom-Hotel, You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself.